Field of the Disclosure
The present invention is related in general to vibration mitigation systems, and in particular to a vibration mitigation device that incorporates a reciprocating assembly connected with a biasing member to mitigate vibration.
Description of the Related Art
Traffic signals are used extensively all over the world to control conflicting flows of traffic. The traffic signals are attached to tall traffic signal poles and horizontally extending mast arms or cables to ensure clear visibility of traffic signals for the drivers or pedestrians. Various types of signal support structures are currently employed, of which cantilevered support structures are widely used as traffic signal support structures since they consist of less material with only one vertical pole. However, cantilevered structures are flexible, lightly-damped structures that are highly susceptible to wind-induced vibration. The sustained large amplitude deflections due to excessive wind-induced vibrations can result in fatigue failure of the mast arm and vertical pole connection. This fatigue failure will ultimately lead to failure of these structures and represents a significant cost to signal owners.
Reducing the effective stress range in the structure by reducing the amplitude of the vibration can significantly increase the life of that structure. This can be done by increasing the damping of the structure with an effective damping device that would decrease the amplitude and number of cycles, thus extending the service life of the structure. A number of different methods have been suggested to increase the damping of the structure and reduce the excessive wind induced vibration of traffic poles. One such method employs a Signal Head Vibration Absorber (SHVA), which is a promising type of vibration absorber for traffic signal support structures.
This device has been experimentally shown to increase the critical damping ratio of the traffic signal structures from less than 1% to over 10%, virtually eliminating any vibration, and protecting the structure from fatigue damage.
In a known prior art related to the vibration dampening systems, the damping assembly employs multiple doughnut shaped metal discs or weights vertically and loosely arranged in a unique fashion about a rod, disposed in a housing within the pole to reduce vibrations. However, the damper requires larger diameter poles which in turn would result in an over-sized support structure. Additionally, this class of damper, based on friction and/or impact damping, is amplitude dependent and may not be effective over certain ranges of vibration amplitudes.
Recent advancements in the art provide a vibration absorber, the SHVA noted above, for traffic signal supports. The SHVA utilizes the mass of the signal head in a configuration as a damped vibration absorber. The system also includes a spring and damper in mechanical communication with the signal head. However, the downside to this system is that the absorber requires utilization of the mass of the traffic signal which itself plays a critical function and the SHVA unit contains components exposed to the elements which requires regular maintenance.
Based on the foregoing there is a need for a vibration mitigation device which utilizes viscous or velocity dependent damping for energy dissipation, eliminates the utilization of the mass of the traffic signal and is self-contained with all critical components protected from the elements. Such a needed device would comprise a reciprocating assembly connected to a biasing member. The device would utilize a tension spring or a compression spring in an eddy current dampening process and/or a pneumatic process to dissipate energy and reduce vibrations. The present invention overcomes prior art shortcomings by accomplishing these critical objectives.